1. Field of the Invention
The present invention relates to an image recording device, an image recording method and a program.
2. Description of the Related Art
In general, when recording digital image data in a recording medium, a gradation depth (also referred to as a bit depth) of the image data to be recorded is determined according to an encoding method complying with the recording medium. For example, when using a Blu-ray Disc™ (BD) and a DVD as the recording medium, an 8-bit gradation depth is used for each color of YUV and the like. However, a gradation depth of the image data to be recorded is not necessarily 8 bits, and in a field of contents creation including authoring, for example, when image quality is especially important, image data having 10-bit or higher gradation depth for each YUV may be handled. In this case, image data with a high gradation depth is quantized such that the gradation depth changes into 8 bits, for example, when being recorded in the above-described recording medium.
By performing such a quantization process, data amount may be reduced by bit cut off, while image quality might be deteriorated, that is to say, smooth gradation characteristics are lost and false contour (color banding) may occur, for example. In this regard, a method such as a systematic dithering method for modulating an error generated by the quantization process into a band with relatively low sensitivity of human visual characteristics or an error diffusion method is known. By using the method such as the systematic dithering method or the error diffusion method, the image quality deterioration perceived by the user may be inhibited to a certain degree. Further, according to the method disclosed in the Japanese Patent Application Laid-Open No. 2009-81848, it is possible to inhibit the image quality deterioration perceived by the user by performing noise shaping having amplitude characteristics similar to inverse characteristics of human vision and while inhibiting a hunting phenomenon.
Also, as techniques to inhibit an image quality deterioration perceived by a user by another approach, technique to expand the gradation depth so as to obtain better image quality when reproducing an image data recorded in a recording medium is suggested (for example, refer to the Japanese Patent Application Laid-Open Nos. H09-219833 and 2008-306656).